Aluminum ethyl phosphite is described in U.S. patent application Ser. No. 531,387 filed on Dec. 10, 1974 as the active agent of fungicidal compositions usable to protect plants. Since this product has proved useful, an industrial manufacturing process was sought.
It is known that aluminum ethyl phosphite may be prepared by dealkylating a phosphite dialkyl by means of a salt, particularly an aluminum chloride. (of V.V. Orfovski et. al., Journal of Gen. Chem. USSR Vol. 42 p 1927-1972)
It has also been proposed that aluminum ethyl phosphite be prepared in a two-stage process: first, saponification by an alkaline hydroxide, in particular soda, of diethyl phosphite to obtain sodium ethyl phosphite, which is then subjected to a double exchange reaction in the presence of a water-soluble aluminum salt. (of U.S. patent appln. Ser. No. 531,387)
It is also known that metal salts of phosphorus monoesters with an alkyl chain containing 1 to 4 carbon atoms may be prepared by reaction, in an anhydrous environment and in the absence of solvents, of a metallic hydroxide at a temperature of about 90.degree. to 150.degree. C. with a dialkyl phosphite. In fact, no illustration of this process is given in the case of preparation of aluminum ethyl phosphite. (of German patent appln. No. 2513965)
When the attempt is made to react diethyl phosphite, which for convenience will be called by its abbreviation DIEP in the remainder of the specification, with hydrated alumina, it is found that hydrolysis is carried out in the proper manner only at temperatures about 150.degree. C. and gives rise to a small portion of monoethyl phosphite (MEP) which indubitably plays the role of catalyst so that an aluminum ethyl phosphite with variable appearance and characteristics is obtained. These two properties render the process utterly unusable on an industrial scale.
It is also known that MEP reacts with alumina at a moderate temperature (80.degree. C.). However, this substance (MEP) has never been prepared and used industrially because of its balanced decomposition into DIEP and phosphoric acid.